The present invention relates to welding devices and methods, and more particularly to Thermit welding.
The preferred embodiments of the present invention refers specifically to a welding device suitable for salvaging metal objects under water. However, the invention may also be used for dry welding, i.e. above the water surface.
The salvaging of underwater objects is an expensive, complex, and frequently dangerous undertaking. Conventional electrical arc underwater welding may be employed, but is rather expensive. Electrical welding underwater requires a large power source and personnel trained in the technique. Due to the water environment, the method frequently yields an inferior weld. The expense and complexity of such welding limits its use to extreme necessity.
Another technique is to utilize a diver, who may secure grappling means to the objects to be salvaged so that it can be raised to the surface. However, divers are not able to descend to depths greater than 1000 feet below the water surface, even employing recent developments in saturated diving. Because approximately 95 percent of the entire ocean floor lies at a depth greater than 1000 feet, there is a need for devices and methods suitable for salvaging at such depths. One way to perform such welding is to use a deep submersible, and employ a welding process which can be controlled remotely.
The use of exothermic welding offers significant advantages. Thermit reactions are relatively simple chemically. Thermit welding devices do not require large power supplies, may be quickly deployed, and, in accordance with the present invention, may be positioned accurately from a remote position, i.e. a submersible. The last-mentioned advantage is of major significance insofar as the welding is accomplished without "feel", that is, there is no weld puddle or arc to be maintained. Thus, exothermic welding is viable at extreme depths.
U.S. Pat. No. 3,871,315 to Andersen discloses a device for Thermit welding which may be attached magnetically to a ferrous object. After the exothermic Thermit reaction initiates, the welding device attaches itself to the ferrous object. Andersen discloses specifically a Thermit materal which has been compressed to about 8,000, psi together with a compressed flux disposed within a cylindrical steel inner housing having an open top. Positioned above the Thermit mixture is a lightly compressed Thermit mixture serving as igniting means, which surrounds a pair of ignition wires. The open end of the housing is capped by a seal, and an outer housing is positioned over the inner housing. A copper ring at the lowermost position of the device serves to retain molten metal as the Thermit burns.
Although the previous device represented a substantial improvement over the art, it had certain drawbacks. First, the Thermit used was compressed to a pressure of approximately 8,000 psi. Achievement of such pressures may be expensive or impractical on a large scale. Accordingly, one object of the present invention is to provide a new method for obtaining a Thermit core with minimal contained surface area and air pockets therein.
Another drawback of previous exothermic devices is the requirement that they be positioned on top of a substantially horizontal surface. For example, in most ocean vessels and in off-shore oil platforms, on "anode" assembly is affixed to a steel surface. This anode is designed to oxide sacrificially, to preserve the steel. The prior art devices for exothermic under water welding are adapted to assist welding of such an anode to a horizontal surface, but not to other orientations. Consequently, a further object is to provide an underwater welding device capable of affixing an anode or other device to surfaces in any plane. further, it is an object to provide for underwater repairs involving welding to surfaces in any plane.
After the Thermit of the previous device retracted and welded, there was a possibility that seawater would enter and rapidly cool the weldment. Accordingly, another object of the invention is to provide a device which will insulate the weldment from seawater, thereby to improve the weld strength by affording an annealing time.
A further drawback with the previous device is the excessive electrical current needed to begin the Thermit reaction. Nickel-chromium wire was disposed within a lightly compressed mixture of fine particle aluminum powder and fine particle iron oxide in proportion by weight of three to seven. The electrical current necessary to institute the reaction of the igniting powder was provided by any means such as a battery from an automobile. While such igniting means was a considerable improvement over the prior art, it has been found that further improvements can be made to render unnecessary the transportation of such cumberous and heavy electrical power source. Accordingly, another object of the present invention is to provide an improved means to intiate Thermit reactions.
Generally, underwater salvaging will involve attaching a suitable device to a ferrous object which is covered by a paint surface. To provide a strong weld, paint or other impurities should be removed from the actual ferrous layer to be welded, and an explosive charge was therefore used to clean the metal surface. A final object of the present invention is to provide improved means for cleaning the surface to be welded.